log

Go language standard library log package implements simple logging.

func main() {
   log.Println("Log message")
   log.Panicln("Panic log")
   log.Fatalln("Error log")
}

Fatal will call os.Exit(1) after writing the log message, while panic will throw a panic.

Prefix

func (l *Logger) Prefix() string // Get prefix

func (l *Logger) SetPrefix(prefix string) // Set prefix

Example:

func main() {
  log.SetPrefix("[main]")
  log.Println("Log message")
  log.Panicln("Panic log")
}

Flag

Methods:

func (l *Logger) Flags() int // Access

func (l *Logger) SetFlags(flag int) // Set

Constants:

const (
   Ldate         = 1 << iota     // Date
   Ltime                         // Time
   Lmicroseconds                 // Microseconds
   Llongfile                     // Full file name
   Lshortfile                    // Short file name
   LUTC                          // Timezone
   Lmsgprefix                    // Prefix
   LstdFlags     = Ldate | Ltime // Initial value
)

Example:

func main() {
   log.SetFlags(log.Lshortfile | log.Lmicroseconds | log.Lmsgprefix | log.Ldate | log.Ltime)
   log.Println("Log message")
   log.Panicln("Panic log")
}

Of course, you can also use log.SetOutput(w io.Writer) to set the log output path, or create your own instance through the New method.

func New(out io.Writer, prefix string, flag int) *Logger

In short, the standard library's log package does not provide complete functionality. We usually use more complete third-party logging packages, such as zap, etc.